Exothermic heats of dilution in non-polar polymer solutions

Abstract

Heats of dilution have been measured calorimetrically, at polymer volume fractions and segment fractions (ϕ₂) less than ∼0.5, for polyisobutene (PIB)+ n-pentane, PIB + cyclohexane, polystyrene (PS)+ methyl ethyl ketone, PS + ethylbenzene and PS + toluene. The heats are negative, apparently reflecting the importance of an equation of state effect. The _χH parameter is independent of ϕ₂, except for PS + toluene where _χH becomes more negative with increasing ϕ₂, confirming results of Lewis and Johnson. The recent Flory theory, and others consistent with the corresponding states principle of Prigogine, predicts a change of sign of _χH from negative to positive with increasing ϕ₂. These results, with the corresponding _χS results obtained using published _χ values appear to indicate an inadequacy in the treatment of the equation of state effect in these theories.